You can be asked to write the electron configuration of atoms and ions for the first 36 elements, so practise, practise these... write down the spd for atoms/ions of your choice and check your answers for the electron configurations of atoms on David Whizzy's Periodic Table
You may need to activate and run JAVA with permission to allow this animated Periodic table to work - it IS worth it!
NCEA PAST EXAMINATION QUESTIONS ON DESCRIBING AND EXPLAINING TRENDS IN THE PERIODIC TABLE
1. Trends in Atomic and Ionic Radi
Explain the difference between the radii of the K atom and the K+ ion.
Discuss the data for the following
Justify why a chloride ion, Cl–, is larger than a chlorine atom, Cl, whereas a sodium ion, Na+, is smaller than a sodium atom, Na.
Match the atoms and ions in the table below to the given radii: Radii: 77 pm 123 pm 128 pm Justify your answer.
State which has the larger radius, Al or Al3+ Justify your answer.
Match the atoms and ions in the table below to the radii given.Radii 99 pm 137 pm 197 pm Justify your answer
Account for the difference in atomic or ionic properties given in the table below
1) Place the following species in order of increasing size: H, H+, H–. Justify your answer
2 ) A bromine atom, Br, has more electrons than a scandium atom, Sc, but its radius is smaller. Explain
Explain the difference between the radii of the following species.
i) K atom and K+ ion
ii) P atom and P3– ion
Compare the relative sizes of the Ca2+ and Cl– ions, and explain the difference in their radii.
Define First ionisation energy: The following table shows the first ionisation energy values for elements in the third period of the periodic table.
Justify the periodic trend of first ionisation energies shown by the data in the table above, and relate this to the expected trend in atomic radii across the third period.
The following table shows the electron configurations of four atoms, He, B, N, and Ne. Arrange these atoms in order of increasing first ionisation energy
Discuss the data for the following
A chlorine atom has a greater first ionisation energy than a sodium atom.
i) Write a balanced ion-electron equation to show the first ionisation of lithium.
ii) With reference to the graph below, discuss the general trends in ionisation energies from lithium to sodium, and account for any anomalies.
Account for the differences in the atomic properties given below
A bromine atom, Br, is smaller than a scandium atom, Sc, but its ionisation energy is larger.
i) Describe what is meant by “the first ionisation energy of chlorine”.
ii) Place magnesium, calcium and chlorine atoms in order of increasing first ionisation energies (IE). Justify your answer in terms of the factors that affect ionisation energy.
Please note: For Excellence answers requiring a discussion of trends be sure to refer to1) nuclear charge2) number of energy levels3) electron-electron repulsion
Now, try these quick revision questions on trends in the Periodic table
NCEA EXAM QUESTION: Describing and Explaining shapes and polarity. In your answer, you must make reference to the arrangement of electrons...
The Lewis diagrams and shapes for XeO2F2and GeH4are shown below.
Compare and contrast the polarities and shapes of these two molecules.
Indicate the polarity of the following bonds by indicating any dipoles present. F - Cl, At - Cl
The Lewis diagrams for SF4 and XeF4 are shown below.
Compare and contrast the polarities and shapes of these two molecules.
The Lewis structures for the two molecules PCl3 and PCl5 are shown below. Compare & contrast the shapes & the polarities of these two molecules.
The Lewis diagrams for ClF3 and AsF5 are shown below. Compare and contrast the shape and polarity of these molecules.
The Lewis diagrams for IF5 and PCl5 are shown below. Discuss the polarities of these molecules.
Discuss the fact that although both SF4and XeF4have four bonds around the central atom, the molecules have different shapes and polarities.
Compare the polarities of the two molecules, BrF3 and SF6
a) The drawings below are three possible shapes for a molecule ZF4, where ‘Z’ represents the central element. ‘Z’ has lower electronegativity than F. Name the shapes represented by the three diagrams.
Explain why C is the only shape that can give rise to a polar molecule for ZF4.
b) i) Draw the Lewis diagram for the ion BrF4–
ii) Choose the structure for the BrF4–ion from those pictured in part (a), on the previous page. Give a reason for your answer.
c) Circle the element, from the following list, which would be the central element Z in a molecule ZF4 that has shape C (see part(a)). Be C Se Si Xe Justify your answer.
Discuss the polarities of AsF3 and AsF5 molecules. Your discussion should include:
- justification for the molecular shape and
- relative electronegativies of the atoms within the molecule.
The Lewis structures for each molecule are shown below.
Discuss reasons for the difference in the polarities of BF3 and PF3 molecules.
i) Calculate the standard enthalpy of formation of liquid ethanol using the information given above
ii) Discuss how the value of the enthalpy change would differ if the ethanol product formed was a gas rather than a liquid. No calculation is necessary.
When gaseous hydrogen and oxygen are heated in a test tube, droplets of liquid water form on the sides of the test tube. Calculate
Δf H°(H2O(ℓ)), given the following data:
Δf H °(H2O(g)) = – 242 kJ mol–1
Δvap H °(H2O(ℓ)) = + 44 kJ mol–1
Ammonia can be oxidised to produce nitrogen, N2, and steam as shown in the equation below:
NCEA EXAM QUESTIONS: Carry out the following questions on Calorimetry
i) When 25.0 mL of a 1.00 mol L–1 hydrochloric acid solution, HCl, is added to 25.0 mL of a 1.00 mol L–1 ammonia solution, NH3, a temperature rise of 6.50°C is recorded, as a neutralisation reaction occurs to produce aqueous ammonium chloride and water. Calculate Δr H ° for this neutralisation reaction. The mass of the mixture is 50.0 g. Assume specific heat capacity of the aqueous ammonium chloride = 4.18 J g–1 °C–1
ii) When the Δr H ° for the neutralisation above was found experimentally in a school laboratory, the value obtained was lower than the theoretical value. Account for the difference in values, and suggest how this difference could be minimised.
The Δc H ° of propene was found experimentally in a school laboratory to be –1 368 kJ mol–1.
The theoretical value is –2 058 kJ mol–1. Account for the difference in values, and suggest how this difference could be minimised.
The apparatus below was used to determine the enthalpy of combustion of hexane. When 0.400 g of hexane was burned in the spirit burner, the temperature of 150 g of water was found to increase from 22°C to 39°C. Calculate the experimental value of ΔcH (C6H14, ℓ). SHC of water = 4.18 J g–1 °C–1
Account for the difference between the experimental value and the value given in a data book as ( - 4163kJmol-1) AND suggest how this difference could be minimised.
Dissolving of ammonium nitrate in water is an endothermic process.
NH4NO3(s) → NH4+(aq) + NO3–(aq)
When 1.80 g of ammonium nitrate was dissolved in 50.0 g of water, the temperature decreased by 2.70°C. The heat capacity of water is 4.18 J g–1°C–1
(i) Calculate the enthalpy change when one mole of ammonium nitrate dissolves completely in water.
(ii) Calculate the mass of ammonium nitrate that would be required to absorb 1.25 kJ of energy.
The diagram below shows a simple calorimeter. It can be used to measure the enthalpy of combustion of ethanol, C2H5OH. If 1.00 g of ethanol is burned in the spirit burner, the temperature of the 200 g of water is found to increase from 22°C to 40°C.
Using these results, calculate the experimental value of ∆cH (C2H5OH, l). Specific heat capacity of water = 4.18 J g–1 °C–1
Give two reasons why the experimental value for the enthalpy of combustion of ethanol calculated in part (a) is so much less than the ‘accepted’ value in data books
The equation for the combustion of pentan-1-ol is:
C5H12O(l) + 7½ O2(g) → 5CO2(g) + 6H2O(l)
Calculate ΔcH ° for pentan-1-ol, given the following data:
Δf H ° (C5H12O(l)) = −295 kJ mol–1
Δf H ° (CO2(g)) = −394 kJ mol–1
Δf H ° (H2O(l)) = −286 kJ mol–1
An equation for the reaction of ammonia gas with hydrogen chloride gas is: NH3(g) + HCl(g) → NH4Cl(s) Calculate the standard enthalpy change, ΔrH°, for this reaction, using the following data. Δf H° (NH3(g)) = –46 kJ mol–1 Δf H° (HCl(g)) = –92 kJ mol–1 Δf H° (NH4Cl(s)) = –314 kJ mol–1
Decane is a component of petrol. Carbon dioxide and water are formed when decane burns completely in oxygen. C10H22(ℓ) + 15 ½ O2(g) → 10CO2(g) + 11H2O(ℓ)
Calculate ΔcH ° (C10H22 (ℓ)), given the following data:
Δf H ° (C10H22(ℓ)) = –250 kJ mol–1
Δf H ° (CO2(g)) = –393 kJ mol–1
Δf H °(H2O(ℓ)) = –286 kJ mol–1
Ammonia gas can be oxidised to produce nitrogen monoxide, NO, and water as shown in the equation below: 4NH3(g) + 5O2(g) --> 6H2O(l) + 6H2O(l)
Calculate the enthalpy change, for this reaction using the information given below.
N2(g) + 3H2(g) --> 2NH3(g) H = –92 kJ mol–1
2H2(g) + O2(g) --> 2H2O(g) H =–484 kJ mol–1
N2(g) + O2(g) --> 2NO(g) H = +180 kJ mol–1
H2O(l) --> H2O(g) H = +41 kJ mol–1
2) An equation for the combustion of octane is: 2C8H18(ℓ) + 25O2(g) → 16CO2(g) + 18H2O(ℓ) Calculate ΔcH °(C8H18(ℓ)), given the following data:
Δf H °(C8H18(ℓ)) = –250 kJ mol–1
Δf H °(CO2(g)) = –394 kJ mol–1
Δf H °(H2O(ℓ)) = –286 kJ mol–1
a) The equation for the combustion of ethanol is: C2H5OH(ℓ) + 3O2(g) → 2CO2(g) + 3H2O(ℓ) Calculate ΔcH ° (C2H5OH (ℓ)), given the following data:
Δf H ° (C2H5OH(ℓ)) = –277 kJ mol−1
Δf H ° (CO2(g)) = −394 kJ mol−1
Δf H ° (H2O(ℓ)) = −286 kJ mol−1
b) Use the information below to show that the Δc H ° of propene, CH2=CHCH3(g), is –2 058 kJ mol–1.
Predict the entropy change for each of the following reactions by stating whether the entropy will increase OR decrease. Give a reason for each answer.
i) Ammonium chloride solid NH4Cl(s) dissolves in water to form NH4+(aq) and Cl–(aq).
a)Ammonium nitrate is used in ‘cold packs’ to relieve symptoms of a sports injury. The dissolving of the solid crystals of ammonium nitrate (shown in the equation below) is spontaneous, despite being endothermic. Explain why this is so, in terms of the entropy change for the reaction system.
NH4NO3(s) → NH4+(aq) + NO3¯(aq)
b) Ammonium nitrate dissociates in an endothermic reaction, as shown in the equation below.
NH4NO3(s) → NH3(g) + HNO3(g)
Below is a table outlining four statements about changes in entropy that may occur during any reaction.
Tick to the left of any statement that is correct for the above reaction. Justify your answer.
Hydrazine is often used as a rocket fuel. When liquid hydrazine undergoes combustion, it forms nitrogen and water:
NCEA EXAM QUESTION: Relating boiling point to intermolecular forces
The two molecules below have the same molecular formula (C5H12O) but have different boiling points.
(i) List all the forces of attraction between these molecules in each of their liquid states.
(ii) Use the information above to explain the difference in the boiling points of pentan-1-ol and dimethylpropan-1-ol by comparing and contrasting the relative strengths of the attractive forces between the molecules involved.
1) The boiling points of ammonia, NH3, fluorine, F2, and hydrogen chloride, HCl, are given in the table below. Complete the table to identify the attractive forces between the molecules in their liquid state.
b)
b) Discuss the differences between the boiling points of NH3and HCl, in terms of the strength of the attractive forces between the particles involved. Then describe why F2has the lowest boiling point.
2)The following graph shows the change in temperature over a five-minute period for a sample of ammonia, where a constant amount of heat was applied per minute.
Using the graph above, justify the physical changes occurring to ammonia between points A and D, in terms of the energy of the particles and the intermolecular forces of attraction.
a) Explain why the temperature of liquid water does not change when it is heated at 100°C.
b) Use the information in the table above to compare and contrast the boiling points of hydrazine, fluoromethane, and decane in terms of the relative strengths of the attractive forces between the particles involved
Use the information in the table to answer the following question.
Compare and contrast the boiling points of water, oxygen, and hydrogen sulfide in terms of the similarities and differences in the relative strengths of the attractive forces present between particles.
Chloroethanol (HOCH2CH2Cl) and chloropropane (CH3CH2CH2Cl) have similar molar masses, but significantly different boiling points.
Identify the substance with the higher boiling point, and justify your choice.
Discuss the trend in boiling points shown in the graph below for the Group 16 hydrides.
In your discussion:
• explain why H2O has a much higher boiling point than the other hydrides
• account for the rise in boiling points from H2S to H2Te
• compare the boiling points of H2S, H2Se and H2Te, and explain the observed trend in terms of bonding AND mass.
a) Ethanol (CH3CH2OH) and propane (CH3CH2CH3) have similar molar masses but ethanol is a liquid at room temperature, while propane is a gas.
Identify the types of intermolecular forces for each of these substances and explain why ethanol has a higher boiling point than propane.
b) Account for the difference in the boiling points of the two substances in the table below by comparing all the intermolecular forces.
Justify the similarity in the ΔvapH ° of CH3Cl and CH3NH2.
Account for the difference in the boiling points for the following pairs of compounds by comparing the main forces between the molecules in each case.
i)
ii)
The boiling points of HF, F2 and HCl are given below.
Discuss the different boiling points of hydrogen fluoride, fluorine and hydrogen chloride in terms of the relative strengths of the intermolecular forces between the particles involved.
Use the following information to answer the question below.
Discuss the trend in DvapH of the compounds in the table above in terms of the attractive forces between the particles and the factors affecting those forces.
Discuss the nature of the forces between molecules in each of the three substances given in the table below, and account for the variation in the melting points.
A chemistry textbook was found to include a table showing the following information.
(a) Describe what is meant by the term DfusH °.
(b) A knowledge of the nature of the substances in the table would indicate that the row of data for one of the substances is obviously incorrect.
Name this substance.
Discuss the nature of bonding in the substances named in the table above, and hence clearly explain why the row of data values can be identified as incorrect.
Ask your teacher to show this Classroom Media award winning video to you as an excellent summary of bonding.
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"Atom Bond - The atom with the golden electron"
In this award-winning animated parody of a James Bond movie, special agent Gold Metallic Bond investigates why Carbon, Nitrogen and other atoms are training themselves in other types of bonds. He uncovers their bond school, learns that they are working towards Project D and ends up being shown around a giant DNA. The cliches and puns from the bond movies are used to bring to life topics including different types of bonding, how and why different atoms bond together, and the results of atoms bonding.
Download this FREE preview of a SUPERB Level 3 Chemistry workbookContinuing Chemistry (2013) Anne Wignall and Terry Wales, Pearson PublishersAnswers included at the back of the book too (Thank you!)
ELECTRON CONFIGURATION OF ATOMS AND IONS
NCEA PAST EXAM QUESTION: Write the electron configuration using s,p,d notation for:
You can be asked to write the electron configuration of atoms and ions for the first 36 elements, so practise, practise these... write down the spd for atoms/ions of your choice and check your answers for the electron configurations of atoms on David Whizzy's Periodic Table
You may need to activate and run JAVA with permission to allow this animated Periodic table to work - it IS worth it!
NCEA PAST EXAMINATION QUESTIONS ON DESCRIBING AND EXPLAINING TRENDS IN THE PERIODIC TABLE
1. Trends in Atomic and Ionic Radi
Explain the difference between the radii of the K atom and the K+ ion.
Discuss the data for the following
Justify why a chloride ion, Cl–, is larger than a chlorine atom, Cl, whereas a sodium ion, Na+, is smaller than a sodium atom, Na.
Match the atoms and ions in the table below to the given radii: Radii: 77 pm 123 pm 128 pm Justify your answer.
State which has the larger radius, Al or Al3+ Justify your answer.
Match the atoms and ions in the table below to the radii given.Radii 99 pm 137 pm 197 pm Justify your answer
Account for the difference in atomic or ionic properties given in the table below
1) Place the following species in order of increasing size: H, H+, H–. Justify your answer
2 ) A bromine atom, Br, has more electrons than a scandium atom, Sc, but its radius is smaller. Explain
Explain the difference between the radii of the following species.
i) K atom and K+ ion
ii) P atom and P3– ion
Compare the relative sizes of the Ca2+ and Cl– ions, and explain the difference in their radii.
2. Trends in Ionisation Energy
Define First ionisation energy: The following table shows the first ionisation energy values for elements in the third period of the periodic table.
Justify the periodic trend of first ionisation energies shown by the data in the table above, and relate this to the expected trend in atomic radii across the third period.
The following table shows the electron configurations of four atoms, He, B, N, and Ne. Arrange these atoms in order of increasing first ionisation energy
Discuss the data for the following
A chlorine atom has a greater first ionisation energy than a sodium atom.
i) Write a balanced ion-electron equation to show the first ionisation of lithium.
ii) With reference to the graph below, discuss the general trends in ionisation energies from lithium to sodium, and account for any anomalies.
i) Describe what is meant by “the first ionisation energy of chlorine”.
ii) Place magnesium, calcium and chlorine atoms in order of increasing first ionisation energies (IE). Justify your answer in terms of the factors that affect ionisation energy.
Using your knowledge of trends in the periodic table, circle the atom below that has the greater electronegativity value. Justify your answer.
Br IDiscuss the data for the following
Account for the differences in electronegativity values for nitrogen, potassium and arsenic
Summary of Trends in the Periodic Table
Now, try these quick revision questions on trends in the Periodic table
SHAPES OF MOLECULES
First, recap on Lewis structures
Now, view Shapes of Molecules in 3D
NCEA EXAM QUESTION: For each of the molecules shown in the table above,
i) draw a 3dimensional (3D) arrangement of the atoms in each molecule
ii) name the shape of each molecule
iii) state the bond angles
Download Powerpoint Level 3 Summary of shapes of molecule
EXPLAINING SHAPE AND POLARITY OF MOLECULES
NCEA EXAM QUESTION: Describing and Explaining shapes and polarity. In your answer, you must make reference to the arrangement of electrons...
The Lewis diagrams and shapes for XeO2F2and GeH4are shown below.
Compare and contrast the polarities and shapes of these two molecules.
Indicate the polarity of the following bonds by indicating any dipoles present. F - Cl, At - Cl
The Lewis diagrams for SF4 and XeF4 are shown below.
Compare and contrast the polarities and shapes of these two molecules.
The Lewis structures for the two molecules PCl3 and PCl5 are shown below. Compare & contrast the shapes & the polarities of these two molecules.
The Lewis diagrams for ClF3 and AsF5 are shown below. Compare and contrast the shape and polarity of these molecules.
The Lewis diagrams for IF5 and PCl5 are shown below. Discuss the polarities of these molecules.
Discuss the fact that although both SF4and XeF4have four bonds around the central atom, the molecules have different shapes and polarities.
Compare the polarities of the two molecules, BrF3 and SF6
a) The drawings below are three possible shapes for a molecule ZF4, where ‘Z’ represents the central element. ‘Z’ has lower electronegativity than F. Name the shapes represented by the three diagrams.
Explain why C is the only shape that can give rise to a polar molecule for ZF4.
b) i) Draw the Lewis diagram for the ion BrF4–
ii) Choose the structure for the BrF4–ion from those pictured in part (a), on the previous page. Give a reason for your answer.
c) Circle the element, from the following list, which would be the central element Z in a molecule ZF4 that has shape C (see part(a)). Be C Se Si Xe Justify your answer.
Discuss the polarities of AsF3 and AsF5 molecules. Your discussion should include:
- justification for the molecular shape and
- relative electronegativies of the atoms within the molecule.
The Lewis structures for each molecule are shown below.
Discuss reasons for the difference in the polarities of BF3 and PF3 molecules.
NCEA EXAM QUESTION: Describing and Explaining Enthalpy changes
(a) The equation for Δf H ° of H2O(l) is:
H2(g) + ½O2(g) → H2O(l) −286 kJ mol–1
(a) (i) Write the equation for ΔcH ° (H2(g)).
(ii) Using the equations above, explain why ΔcH ° (H2) and Δf H ° (H2O) have the same value of −286 kJ mol–1.
(b) The enthalpy of formation would change if the water was formed as a gas rather than a liquid.
(i) Circle the correct phrase to complete the sentence below.
ΔfH ° (H2O(g)) is: less negative than / the same as / more negative than ΔfH ° (H2O()).
(ii) Justify your choice.
Explain what is meant by the term Δvap H ° (H2O(ℓ)).
i) Write an equation for the reaction that represents the heat of combustion of sulfur (S, s).
ii) Explain why (S, s) and (SO2, g) have the same value.
i) Explain what is meant by the symbol ΔcH °
ii) Write the equations which represent the enthalpy of fusion, ΔfusH °, and vaporisation, ΔvapH °, for water.
iii) Explain why ΔvapH °(H2O) = 40.7 kJ mol–1 is greater than ΔfusH °(H2O) = 6.01 kJ mol–1.
In your answer you should include:
• a description of the attractive forces between the molecules in the different phases (states) of water
• a discussion of how these forces relate to the given enthalpy values.
i) Explain what is meant by the term ΔvapH °.
ii) Explain why Δf H ° (CO2(g)) and Δc H ° (C(s)) have the same value of −394 kJ mol−1.
i) Write the equation for which the enthalpy change is the enthalpy of formation, Δf H°, for zinc oxide.
(ii) Write the equation for which the enthalpy change is the enthalpy of fusion, ΔfusH°, for zinc sulfide.
(iii) Give a reason why ΔfusH° is always greater than zero.
Define the term ΔvapH °.
Urea, (NH2)2CO, which is a white crystalline solid, is widely used as a fertiliser. Write the equation for which the enthalpy change is:
(i) the enthalpy of formation, ΔfH°, for urea
(ii) the enthalpy of fusion, ΔfusH°, for urea
Write the equation for the reaction that has an enthalpy change given by Δ fH°(HCl, g).
i) Write the equation for the reaction that has an enthalpy change equal toΔcH (H2, g)
ii) Explain why ΔfH(H2O, ℓ) is equal to ΔcH(H2, g).
NCEA EXAM QUESTION: Enthalpy Change Calculations
Calculate the ΔfH ° for B2H6(g), given the following data:
Δf H ° (B2O3(s)) = −1255 kJ mol–1
Δf H ° (H2O(l)) = −286 kJ mol–1
B2H6(g) + 3O2(g) → B2O3(s) + 3H2O(l) Δr H ° = −2148 kJ mol–1
The melting point of boron is 2300°C.
i) Calculate the standard enthalpy of formation of liquid ethanol using the information given above
ii) Discuss how the value of the enthalpy change would differ if the ethanol product formed was a gas rather than a liquid. No calculation is necessary.
When gaseous hydrogen and oxygen are heated in a test tube, droplets of liquid water form on the sides of the test tube. Calculate
Δf H°(H2O(ℓ)), given the following data:
Δf H °(H2O(g)) = – 242 kJ mol–1
Δvap H °(H2O(ℓ)) = + 44 kJ mol–1
Ammonia can be oxidised to produce nitrogen, N2, and steam as shown in the equation below:
4NH3(g) + 3O2(g) --> 2N2(g) + 6H2O(g) = -1267 kJ mol–1
Calculate the energy produced when 50.0 g of ammonia reacts as shown in the equation above.
Δ fH°(HBr, g) is –36.2 kJ mol–1. Calculate the heat produced by the formation of 50.0 g of HBr(g) from its elements in their standard states.
The experimental value for ΔfH°(H2O, ℓ) is –286 kJ mol–1.
Using the information above, calculate the ΔvapH°(H2O), and also the heat required to vapourise 100 g of water.
CALORIMETRY
NCEA EXAM QUESTIONS: Carry out the following questions on Calorimetry
i) When 25.0 mL of a 1.00 mol L–1 hydrochloric acid solution, HCl, is added to 25.0 mL of a 1.00 mol L–1 ammonia solution, NH3, a temperature rise of 6.50°C is recorded, as a neutralisation reaction occurs to produce aqueous ammonium chloride and water. Calculate Δr H ° for this neutralisation reaction. The mass of the mixture is 50.0 g. Assume specific heat capacity of the aqueous ammonium chloride = 4.18 J g–1 °C–1
ii) When the Δr H ° for the neutralisation above was found experimentally in a school laboratory, the value obtained was lower than the theoretical value. Account for the difference in values, and suggest how this difference could be minimised.
The Δc H ° of propene was found experimentally in a school laboratory to be –1 368 kJ mol–1.
The theoretical value is –2 058 kJ mol–1. Account for the difference in values, and suggest how this difference could be minimised.
The apparatus below was used to determine the enthalpy of combustion of hexane. When 0.400 g of hexane was burned in the spirit burner, the temperature of 150 g of water was found to increase from 22°C to 39°C. Calculate the experimental value of ΔcH (C6H14, ℓ). SHC of water = 4.18 J g–1 °C–1
Account for the difference between the experimental value and the value given in a data book as ( - 4163kJmol-1) AND suggest how this difference could be minimised.
Dissolving of ammonium nitrate in water is an endothermic process.
NH4NO3(s) → NH4+(aq) + NO3–(aq)When 1.80 g of ammonium nitrate was dissolved in 50.0 g of water, the temperature decreased by 2.70°C. The heat capacity of water is 4.18 J g–1°C–1
(i) Calculate the enthalpy change when one mole of ammonium nitrate dissolves completely in water.
(ii) Calculate the mass of ammonium nitrate that would be required to absorb 1.25 kJ of energy.
The diagram below shows a simple calorimeter. It can be used to measure the enthalpy of combustion of ethanol, C2H5OH. If 1.00 g of ethanol is burned in the spirit burner, the temperature of the 200 g of water is found to increase from 22°C to 40°C.
Using these results, calculate the experimental value of ∆cH (C2H5OH, l). Specific heat capacity of water = 4.18 J g–1 °C–1
Give two reasons why the experimental value for the enthalpy of combustion of ethanol calculated in part (a) is so much less than the ‘accepted’ value in data books
HESS'S LAW
NCEA EXAM QUESTION: Hess's Law Calculations
The equation for the combustion of pentan-1-ol is:
C5H12O(l) + 7½ O2(g) → 5CO2(g) + 6H2O(l)
Calculate ΔcH ° for pentan-1-ol, given the following data:
Δf H ° (C5H12O(l)) = −295 kJ mol–1
Δf H ° (CO2(g)) = −394 kJ mol–1
Δf H ° (H2O(l)) = −286 kJ mol–1
An equation for the reaction of ammonia gas with hydrogen chloride gas is: NH3(g) + HCl(g) → NH4Cl(s)
Calculate the standard enthalpy change, ΔrH°, for this reaction, using the following data.
Δf H° (NH3(g)) = –46 kJ mol–1
Δf H° (HCl(g)) = –92 kJ mol–1
Δf H° (NH4Cl(s)) = –314 kJ mol–1
Decane is a component of petrol. Carbon dioxide and water are formed when decane burns completely in oxygen. C10H22(ℓ) + 15 ½ O2(g) → 10CO2(g) + 11H2O(ℓ)
Calculate ΔcH ° (C10H22 (ℓ)), given the following data:
Δf H ° (C10H22(ℓ)) = –250 kJ mol–1
Δf H ° (CO2(g)) = –393 kJ mol–1
Δf H °(H2O(ℓ)) = –286 kJ mol–1
Ammonia gas can be oxidised to produce nitrogen monoxide, NO, and water as shown in the equation below: 4NH3(g) + 5O2(g) --> 6H2O(l) + 6H2O(l)
Calculate the enthalpy change, for this reaction using the information given below.
N2(g) + 3H2(g) --> 2NH3(g) H = –92 kJ mol–1
2H2(g) + O2(g) --> 2H2O(g) H =–484 kJ mol–1
N2(g) + O2(g) --> 2NO(g) H = +180 kJ mol–1
H2O(l) --> H2O(g) H = +41 kJ mol–1
2) An equation for the combustion of octane is: 2C8H18(ℓ) + 25O2(g) → 16CO2(g) + 18H2O(ℓ) Calculate ΔcH °(C8H18(ℓ)), given the following data:
Δf H °(C8H18(ℓ)) = –250 kJ mol–1
Δf H °(CO2(g)) = –394 kJ mol–1
Δf H °(H2O(ℓ)) = –286 kJ mol–1
a) The equation for the combustion of ethanol is: C2H5OH(ℓ) + 3O2(g) → 2CO2(g) + 3H2O(ℓ) Calculate ΔcH ° (C2H5OH (ℓ)), given the following data:
Δf H ° (C2H5OH(ℓ)) = –277 kJ mol−1
Δf H ° (CO2(g)) = −394 kJ mol−1
Δf H ° (H2O(ℓ)) = −286 kJ mol−1
b) Use the information below to show that the Δc H ° of propene, CH2=CHCH3(g), is –2 058 kJ mol–1.
CH2=CHCH3(g) + H2(g) → CH3CH2CH3(g) Δr H ° = –124 kJ mol–1
CH3CH2CH3(g) Δc H ° = –2 220 kJ mol–1
H2O(ℓ ) Δf H ° = –286 kJ mol–1
Zinc oxide is formed when zinc sulfide is heated in air. 2ZnS(s) + 3O2(g) → 2ZnO(s) + 2SO2(g)
Calculate the enthalpy change, ΔrH°, for this reaction, using the following data.
Δf H° (ZnS(s)) = –200 kJ mol–1
Δf H° (ZnO(s)) = –348 kJ mol–1
Δf H° (SO2(g)) = –297 kJ mol–1
Carbon dioxide and water are formed when hexane burns in oxygen
C6H14(ℓ) + 9½O2(g) → 6CO2(g) + 7H2O(ℓ) ΔcH °= – 4163 kJ mol–1
Calculate the enthalpy of formation of hexane, Δf H °(C6H14, ℓ).
Δf H ° (CO2, g) = –393 kJ mol–1
Δf H ° (H2O, ℓ) = –286 kJ mol–1
Urea breaks down in moist soil into carbon dioxide and ammonia.(NH2)2CO(s) + H2O(l) → CO2(g) + 2NH3(g)
Calculate the enthalpy change for this reaction, ΔrH, using the information below.
(NH2)2CO(s) + 3½O2(g) → CO2(g) + 2H2O(l) + 2NO2(g) ΔrH = –632 kJ mol–1
4NH3(g) + 5O2(g) → 4NO(g) + 6H2O(g) ΔrH = –906 kJ mol–1
NO(g) + ½O2(g) → NO2(g) ΔrH = –57 kJ mol–1
H2O(l) → H2O(g) ΔvapH = +41 kJ mol–1
Calculate the heat of combustion of ethyne, DcH° C2H--2(g), from the following data:
2C(s) + H2(g) → C2H2(g) Δ rH° = 229 kJ mol–1
Δ cH° (H-2, g) = –285 kJ mol–1
Δ cH° (C, s) = –393 kJ mol–1
Calculate Δ fH°(C2H5OH, ℓ) using the following data.
Δ cH°(C2H5OH, ℓ) = –1367 kJ mol–1
Δ fH°(CO2, g) = –394 kJ mol–1
Δ fH°(H2O, ℓ) = –286 kJ mol–1
NCEA EXAM QUESTION: Predicting Entropy Change
Predict the entropy change for each of the following reactions by stating whether the entropy will increase OR decrease. Give a reason for each answer.
i) Ammonium chloride solid NH4Cl(s) dissolves in water to form NH4+(aq) and Cl–(aq).
ii) 3O2(g) --> 2O3(g)
iii) N2O4(g) --> 2NO2(g)
NCEA EXAM QUESTION: Explaining Entropy Change
a)Ammonium nitrate is used in ‘cold packs’ to relieve symptoms of a sports injury. The dissolving of the solid crystals of ammonium nitrate (shown in the equation below) is spontaneous, despite being endothermic. Explain why this is so, in terms of the entropy change for the reaction system.
NH4NO3(s) → NH4+(aq) + NO3¯(aq)
b) Ammonium nitrate dissociates in an endothermic reaction, as shown in the equation below.
NH4NO3(s) → NH3(g) + HNO3(g)
Below is a table outlining four statements about changes in entropy that may occur during any reaction.
Tick to the left of any statement that is correct for the above reaction. Justify your answer.
Hydrazine is often used as a rocket fuel. When liquid hydrazine undergoes combustion, it forms nitrogen and water:
N2H4(ℓ) + O2(g) → N2(g) + 2H2O(g) ΔcH°( N2H4 (ℓ)) = –624 kJ mol–1
Explain why liquid hydrazine readily burns in oxygen.
Your answer should consider both enthalpy and entropy changes.
At room temperature, 25ºC, steam condenses to water as shown in the equation below. This reaction occurs spontaneously.
H2O(g) --> H2O(l)
Explain why this reaction is spontaneous by considering the entropy changes when steam condenses.
if you are interested, download some background but not essential information from Chemguide on EntropyINTERMOLECULAR FORCES
NCEA EXAM QUESTION: Relating boiling point to intermolecular forces
The two molecules below have the same molecular formula (C5H12O) but have different boiling points.
(i) List all the forces of attraction between these molecules in each of their liquid states.
(ii) Use the information above to explain the difference in the boiling points of pentan-1-ol and dimethylpropan-1-ol by comparing and contrasting the relative strengths of the attractive forces between the molecules involved.
1) The boiling points of ammonia, NH3, fluorine, F2, and hydrogen chloride, HCl, are given in the table below. Complete the table to identify the attractive forces between the molecules in their liquid state.
b)
b) Discuss the differences between the boiling points of NH3and HCl, in terms of the strength of the attractive forces between the particles involved. Then describe why F2has the lowest boiling point.
2) The following graph shows the change in temperature over a five-minute period for a sample of ammonia, where a constant amount of heat was applied per minute.Using the graph above, justify the physical changes occurring to ammonia between points A and D, in terms of the energy of the particles and the intermolecular forces of attraction.
a) Explain why the temperature of liquid water does not change when it is heated at 100°C.
b) Use the information in the table above to compare and contrast the boiling points of hydrazine, fluoromethane, and decane in terms of the relative strengths of the attractive forces between the particles involved
Use the information in the table to answer the following question.
Compare and contrast the boiling points of water, oxygen, and hydrogen sulfide in terms of the similarities and differences in the relative strengths of the attractive forces present between particles.
Chloroethanol (HOCH2CH2Cl) and chloropropane (CH3CH2CH2Cl) have similar molar masses, but significantly different boiling points.
Identify the substance with the higher boiling point, and justify your choice.
Discuss the trend in boiling points shown in the graph below for the Group 16 hydrides.
In your discussion:
• explain why H2O has a much higher boiling point than the other hydrides
• account for the rise in boiling points from H2S to H2Te
• compare the boiling points of H2S, H2Se and H2Te, and explain the observed trend in terms of bonding AND mass.
a) Ethanol (CH3CH2OH) and propane (CH3CH2CH3) have similar molar masses but ethanol is a liquid at room temperature, while propane is a gas.
Identify the types of intermolecular forces for each of these substances and explain why ethanol has a higher boiling point than propane.
b) Account for the difference in the boiling points of the two substances in the table below by comparing all the intermolecular forces.Justify the similarity in the ΔvapH ° of CH3Cl and CH3NH2.
Account for the difference in the boiling points for the following pairs of compounds by comparing the main forces between the molecules in each case.
i)
ii)
The boiling points of HF, F2 and HCl are given below.
Discuss the different boiling points of hydrogen fluoride, fluorine and hydrogen chloride in terms of the relative strengths of the intermolecular forces between the particles involved.
Use the following information to answer the question below.
Discuss the trend in DvapH of the compounds in the table above in terms of the attractive forces between the particles and the factors affecting those forces.
Discuss the nature of the forces between molecules in each of the three substances given in the table below, and account for the variation in the melting points.
A chemistry textbook was found to include a table showing the following information.
(a) Describe what is meant by the term DfusH °.
(b) A knowledge of the nature of the substances in the table would indicate that the row of data for one of the substances is obviously incorrect.
Name this substance.
Discuss the nature of bonding in the substances named in the table above, and hence clearly explain why the row of data values can be identified as incorrect.
Ask your teacher to show this Classroom Media award winning video to you as an excellent summary of bonding.
27mins
"Atom Bond - The atom with the golden electron"
In this award-winning animated parody of a James Bond movie, special agent Gold Metallic Bond investigates why Carbon, Nitrogen and other atoms are training themselves in other types of bonds. He uncovers their bond school, learns that they are working towards Project D and ends up being shown around a giant DNA. The cliches and puns from the bond movies are used to bring to life topics including different types of bonding, how and why different atoms bond together, and the results of atoms bonding.
Download this FREE preview of a SUPERB Level 3 Chemistry workbookContinuing Chemistry (2013) Anne Wignall and Terry Wales, Pearson PublishersAnswers included at the back of the book too (Thank you!)